DERBY-6193: AutomaticIndexStatisticsTest doesn't delete its single-use database

Delete the extra database on successful completion. Also wrap the test
in a CleanDatabaseTestSetup so that it also cleans up the default
database when it's done.

git-svn-id: https://svn.apache.org/repos/asf/db/derby/code/trunk@1471264 13f79535-47bb-0310-9956-ffa450edef68